In the Sierra I use their maps as a larger-scale route planning tool (for example, I have the TI Yosemite map, but none of the four smaller-scale maps), and find them pretty good for that purpose. I have a large collection of Sierra USGS topo maps I bought, mostly back when they were $2.50/each, that I use hiking. And there are trail location errors on the USGS maps as well.
I only use the TI maps for hiking in places like Yellowstone where permits are for designated campsites which are much better shown on the TI maps.
Edit: Actually, I also used the TI map hiking in Isle Royale NP...permit specifies nothing, use of designated campsites are required (mostly) but TOPO! indicates all are shown adequately on the USGS maps, but it was a choice of one TI map or way too many USGS maps that mostly showed Lake Superior due to the lat/lon square layout of the maps.
Edited 1 time(s). Last edit at 09/21/2011 07:31PM by ttilley.